Japanese Patent Application Publication No. S62-218087 sets forth a basic configuration of a reduction mechanism in which an internal gear and an external gear having a differing number of teeth are provided, and that utilizes the phenomenon of there being a discrepancy in rotation revolutions when the external gear is made to revolve orbitally (oscillate) within the internal gear. This type of reduction mechanism utilizes a crank shaft. An eccentric cam that revolves eccentrically when the crank shaft rotates is fixed to the crank shaft, and an external gear engages with the eccentric cam. The eccentric cam revolves eccentrically when the crank shaft rotates, and the external gear engaged with the eccentric cam revolves orbitally (oscillates).
With this type of reduction mechanism, the internal gear rotates if the rotation of the external gear is restrained. In this case, the internal gear rotates around a carrier. Conversely, the external gear rotates if the rotation of the internal gear is restrained. In this case, the external gear rotates while it is revolving orbitally. An output shaft portion which rotates around the orbital rotation center of the external gear is obtained by utilizing a member that is capable of rotating around the orbital rotation center of the external gear and is capable of supporting the external gear such that the external gear is capable of rotation.
It is often desired, in industrial robots or machine tools, that a rotation shaft of a motor and an output shaft of a reduction mechanism have an orthogonal relationship. The use of this layout often has the advantage of decreasing the overall length of a mechanism in which the reduction mechanism has been combined with the motor.
A mechanism in which an intermediate shaft is disposed orthogonally to an input shaft that is operated by the torque of the motor, and which converts the direction of rotation by joining the input shaft and the intermediate shaft by gears, is often utilized when combined with a reduction mechanism. It is possible to transfer the torque to the intermediate shaft from the input shaft that is disposed orthogonally to this intermediate shaft by meshing a pair of bevel gears or a pair of hypoid gears.
A reduction gear box in which a rotation direction converting part and a reduction part are joined together is taught in Japanese Patent Application Publication No. 2004-293640.